1. Field of the Invention
The present invention relates to a superconducting fault current limiter capable of reducing a fault current in a power application field, such as a lossless power transmission line, a superconductive magnet for generating a strong or very stable magnetic field, an energy storage, a motor, a generator etc., of generating or transporting a large amount of current, and a traffic application field such as a superconducting magnetic levitation train, a superconducting propulsion ship, and so on.
2. Description of the Related Art
A superconducting fault current limiter, which is classified into an inductive type or a resistive type, is an electric power device for instantly generating impedance and sharply lowering fault current when the fault current is generated, while it is operated with a little impedance in a normal state.
The inductive superconducting fault current limiter limits current by mainly using an inductance component as impedance, and the resistive superconducting fault current limiter limits current by mainly using a resistance component as impedance.
In addition, the resistive superconducting fault current limiter generates resistance through rapid phase transition of a superconductor when a fault current is larger than a critical current of the superconducting fault current limiter, and uses the resistance as impedance to limit the fault current.
In particular, the resistive superconducting fault current limiter is a current limiter using a superconducting wire, which is disclosed in U.S. Pat. No. 6,275,365, entitled “Resistive Fault Current Limiter,” and U.S. Pat. No. 6,137,388, entitled “Resistive Superconducting Fault Current Limiter,” '365 and '388 patents employ a method of almost removing an inductance component by offsetting a magnetic flux component generated from one coil by one generated from the other coil.
In this manner, since the superconducting wire allows a large current to flow without loss due to zero resistance characteristics under a critical temperature, it is possible to put to practical use various types of superconducting power equipment, such as a transformer, a motor, a generator, a current limiter etc., using the superconducting wire as a superconducting coil conductor. In addition, the superconducting wire is widely used in various energy, traffic, and environmental industries applying an electric field, for example, a superconducting power storage, a superconducting power transmission cable, a superconducting magnetic levitation train, a superconducting magnetic isolation apparatus, and so on.
However, as shown in FIG. 1, the conventional resistive superconducting fault current limiters disclosed in '365 and '388 patents include a power input terminal IN and a power output terminal OUT, which are located at the same level, and a dielectric distance between ends of the power input and output terminals IN and OUT is very short, thereby generating disadvantages in electrical insulation.
That is, since most of the conventional resistive superconducting fault current limiters have a very short distance between first and final turns to which operational voltage is applied, they are inevitably vulnerable to the insulation.
In addition, since the conventional superconducting fault current limiters have a structure that a superconducting wire or coil 2 wound around a bobbin 1 is stacked as shown in FIG. 2, a temperature may be excessively increased during the phase transition, and a recovering speed of the fault current limiter may be considerably delayed until the next fault current is limited.
Meanwhile, U.S. Pat. No. 5,021,914, entitled “Superconducting Switch and Current Limiter Using such a Switch,” discloses another conventional resistive superconducting fault current limiter using a former made of a glass tube as well as an iron core made of cast iron.
However, in the case of '914 patent, since a low temperature superconducting wire of stabilizer is made of a copper alloy as a main component, the stabilizer has a disadvantage of generating a very low resistance in a quench state of escaping from the superconducting state.
Therefore, the stabilizer of '914 patent requires a very long wire. In addition, the lower temperature superconducting wire has a circular cross-section difficult to be wound around the same frame, and though the wire is wound, a somewhat magnetic leakage flux is generated to make it difficult to expect a perfect non-induction characteristic.
In addition, since '914 patent includes the low temperature superconducting wire, liquid helium should be used as a coolant. However, when the superconducting wire is out of the superconducting state (quench), the liquid helium may be sublimated to remarkably lower insulation resistance. Further, the superconducting wire should be connected in parallel in order to increase a critical current. Nevertheless, '914 patent has no structure capable of connecting the superconducting wire in parallel.